The use of web surveys is a common and popular data collection method in behavioral and social research. Compared to other established survey modes, web surveys are frequently cheaper and less time consuming, because they are commonly self-administered. They also allow respondents to take part with few time and location restrictions. However, research has shown that web surveys are frequently associated with multitasking, which may negatively affect response behavior and response quality. In this study, we use paradata detecting switching away from the web survey to explore on-device media multitasking. We conducted a web survey in an opt-in access panel in Germany and randomly assigned respondents to a PC or smartphone condition. The results reveal that on-device media multitasking is more common on PCs than on smartphones. We also find evidence that engaging in on-device media multitasking affects response quality. Respondents who switch away are more likely to select the middle response category. In addition, the results show that the question presentation format, the device type, and respondents’ age and education are associated with the occurrence of on-device media multitasking. These findings point to the importance of controlling for on-device media multitasking in web surveys.